Shell type magnetron device

ABSTRACT

A magnetron device comprising a magnetron body having a cathode stem and an output antenna section respectively provided projectively from both ends of said body, first and second magnets disposed on the magnetron body with the projecting cathode stem and output antenna section respectively inserted into the magnets and a yoke for magnetically connecting the first and second magnets. The first magnet mounted on the cathode stem side bears a substantially parallelepiped form almost as wide as the outer diameter of the magnetron body and the second magnet provided on the output antenna side presents a thin doughnut shape. That side of the yoke which faces the first magnet is made substantially as wide as the end face of the first magnet and the magnetron body is provided with a plurality of radiator plates erected on the magnetron body in a radial direction, each having a plane parallel with the axis of the magnetron body.

United States Patent [191 Koinuma et al.

[ SHELL TYPE MAGNETRON DEVICE [75] Inventors: Tokuji Koinuma, Kawasaki;

Kaichiro Nakai, Yokohama; Hirosi ldeue, Yokohama; Hiromi Komura, Yokohama; Kazuhisa Nitta, Yokohama, all of .Iapan [73] Assignee: Tokyo Shibaura Electric Co., Ltd., Kawasaki, Japan [22] Filed: July 10, 1974 [21] Appl. No.: 487,148

[ 30] Foreign Application Priority Data July 16, 1973 Japan 48-84102 [52] US. Cl. 315/39.7l; 315/3951; 315/3953 [51] Int. C1. H01J 25/50 [58] Field of Search 315/3951, 39.71, 39.53

[56] References Cited UNITED STATES PATENTS 3,304,400 2/1967 Ojelid 315/39.71 X 3,315,121 4/1967 Staats 315/39.71 X 3,577,033 5/1971 Aoki et al. 315/39.71 3,588,588 6/1971 Numata 315/3971 3,746,916 7/1973 Oguro 315/3971 Oct. 28, 1975 3,794,879 211974 Edwards ..315/39.7l

Primary ExaminerSaXfield Chatmon, Jr. Attorney, Agent, or Firm-Oblon, Fisher, Spivak, McClelland & Maier 57 ABSTRACT A r'nagnetron device comprising a magnetron body having a cathode stem and an output antenna section respectively provided projectively from both ends of said body, first and second magnets disposed on the magnetron body with the projecting cathode stem and output antenna section respectively inserted into the magnets and a yoke for magnetically connecting the first and second magnets. The first magnet mounted on the cathode stem side bearsa substantially parallelepiped form almost as wide as the outer diameter of the magnetron body and the second magnet provided on the output antenna side presents a thin doughnut shape. That side of the yoke which faces the first magnet is made substantially as wide as the end face of the first magnet and the magnetron body is provided with a plurality of radiator plates erected on the magnetron body in a radial direction, each having a plane parallel with the axis of the magnetron body.

7 Claims, 6 Drawing Figures US. Patent Oct. 28, 1975 Sh eetlof2 3,916,247

FIG.

FIG.2

U.S. Patent Oct.28, 1975 Sheet20f 2 3,916,247

FIG.3

Sl-[ELL TYPE MAGNETRON DEVICE BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to a magnetron device, and more particularly to a shell type magnetron device constructed more effectively to cool the magnetron body.

2. DESCRIPTION OF THE PRIOR ART A magnetron device which efficiently generates a large output under a stable condition is most adapted for oscillation of microwaves and consequently is used with a heating, drying and defrosting apparatus based on microwave energy, for example, an electronic oven. A magnetron device is generally divided into a strut type in which magnets are arranged parallel by the side of a magnetron body and a shell type in which magnets are disposed at the topand bottom of the magnetron body with a yoke so fitted as to surround the upper and lower magnets. Though magnetically more efficient due to little leakage of magnetism, yet the shell type magnetron device has the drawback of being cooled less efiectively. Namely, with this type of magnetron device, the flow of cooling air is prominently obstructed by two magnets disposed at the top and bottom of a magnetron body, each having a larger diameter than that of the magnetron body and the yoke extending around said body magnetically to connect both magnets, practically preventing the magnetron device from being cooled. Further the shell type magnetron device is so designed as to conduct cooling air at right angles to the axis of the magnetron, namely, blow cooling air in the horizontal direction. Where, therefore, such type of magnetron device is incorporated in an electronic oven, the arrangement and handling of a cooling device are accompanied with inconvenience. Accordingly, demand has been made to develop such type of magnetron device as causes cooling air to be delivered parallel with the axis of the magnetron device, namely, in the vertical direction.

SUMMARY OF THE INVENTION It is accordingly the object of this invention to provide a shell type magnetron device so constructed as to be effectively cooled.

According to an aspect of this invention, there is provided a' magnetron device wherein a plurality of cooling plates are spatially provided on the peripheral wall of a magnetron body soas to conduct a-cooling medium in the axial direction of said body. Further provided on the cathode stem side of the magnetron body is a first thick polyhedral shape magnet having a width almost equal to the outer diameter of the magnetron body. Disposed on the output antenna side of said body is a second thin magnet. That side of the yoke magnetically connecting the first and second magnets which faces the first magnet has almost the same width as the first magnet.

BRIEF DESCRIPTION OF THE DRAWINGS This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a fractional sectional view of a magnetron device according to an embodiment of this invention; FIG. 2. is a cross sectional view on line 2--2 of FIG.

FIG. 3 is an oblique view of a polyhedral shape magnet provided on the cathode stem side of the magnetron body of FIG. 2;

FIG. 4 is an oblique view of a thin magnet disposed on the output. antenna side of the magnetron body;

FIG. 5 is an oblique view of the yoke; and

FIG. 6 is an oblique view of an assembly of magnets and a yoke included in a magnetron device according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Referring to FIG. 1, the magnetron body 21 comprises a cathode 22 disposed along the axis thereof; a cylindrical anode 24 concentrically provided on the periphery of the cathode 22; a plurality of vanes erected on the inner peripheral wall of the cylindrical anode; and a pair of conical magnetic pole pieces 25, 26 respectively fitted to both ends of the anode 24. A cathode stem 27 and output antenna section 28 are projectively provided at both ends of the anode 24 concentrically with the magnetron body 21. A radiator 29 is provided which comprises a plurality of radiator plates 29c radially erected on the peripheral wall of the anode 24 to conduct cooling air in the axial direction of the magnetron body 21. The radiator 29 may be replaced by a plurality of propeller-shaped radiator units superposed in theaxial direction of the magnetron body 21 and each formed of numerous vanes obliquely arranged relative to the axis of the magnetron body 21. First and second ferrite permanent magnets 30, 31 face the corresponding magnetic pole pieces 25, 26 for magnetic connection with magnetic shims 32, 33 made of magnetic material respectively interposed between the first magnet 30 and corresponding magnetic piece 25, as well as between the second magnet 31 and corresponding magnetic piece 26. The first and second ferrite permanent magnets 30, 31 are disposed on the magnetron body 21 with the planes of opposite magnetic poles made to face each other, thereby enabling a magnetic field created by said permanent magnets 30, 31 to act in the axial direction of the magnetron body 21 in the space thereof where electrons are brought into action. Since the magnetic field should preferably be applied uniformly through the space acted on by electrons, both permanent magnets 30, 31 are desired to have an equal magnetomotive force and in consequence an equal volume, if they are made of the same material. The backsides of both permanent magnets 30, 31 are magnetically connected by integrally combined yoke members 34, 35 which are so disposed as to surround the magnetron body 21 and permanent magnets 30, 31. Those inner walls of the yoke members 34, 35 which abut against the backsides of the permanent magnets 30, 31 are formed with a shape and size resembling said backsides. The yoke member 34 having a smaller abutting area than the yoke member 35 is made thicker than the yoke member 35 in order to strike a balance between their magnetic resistances. A blind cylindrical shield 36 is provided to enclose the abovementioned magnetron assembly. The bottom of the shield 36 facing the cathode stem 27 is so constructed as to prevent the leakage of microwaves and further bored with nu-- The first ferrite permanent magnet 30 so disposed as to surround the cathode stem 27 is bored, as shown in FIG. 3, with a through hole 30a at the center, and bears a polyhedral form, for example, substantially parallelepiped form slightly broadened at the center of the horizontal plane and chamfered at the four corners. The magnet 30 may be made into any desired form for example, ellipse shape or egg shape. The yoke member 34 abutting against the first parallelepiped ferrite permanent magnet 30 presents an inverted U-shape as shown in FIGS. 1 and 5. The upper wall of the yoke member 34 pressed against the first parallelepiped ferrite permanent magnet 30 is bored with a hole 40 corresponding to the through hole 30a of said magnet 30 and has substantially the same width l as the width t of said magnet 30 and also a shape almost equal to the end face thereof. The lengthwise direction of the upper wall of the yoke member 34 is aligned with that of the end face of the first parallelepiped ferrite permanent magnet 30. The magnetic shim 32 made of magnetic material has a shape substantially similar to, but small than, the end face of the first parallelepiped ferrite permanent magenet 30. The width t of the first parallelepiped ferrite permanent magnet 30 and the width 1 of the yoke member 34 are substantially equal to the outer diameter of the magnetic pole piece 25. As apparent from FIG. 2, most of numerous erected radiator plates 29c extending radially from the side of the first parallelepiped ferrite permanent magnet 30 and narrower yoke member 34 receive cooling air, enabling the whole of the magnetron body 21 to be more effectively cooled. A conductive cylindrical member 41 is inserted into the through hole 30a so as to prevent microwaves from being absorbed in the first parallelepiped ferrite permanent magnet 30 or partly permeating it. The second ferrite permanent magnet 31 bears, as shown in FIG. 4, a doughnut shape bored with a through hole 42 at the center and has a larger outer diameter than the width t of the first parallelepiped ferrite permanent magnet 30. The second magnet may be made into any desired form, for example, a nut shape or square shape. The yoke member 35 abutting against the second ferrite permanent magnet 31 is large enough fully to close the end face of said magnet 31. Since a yoke has a magnetic resistance proportional to its cross sectional area, the narrow yoke member 34 is made thicker than the yoke member 35 to strike a balance between their magnetic resistances. The magnetic shim 33 has a smaller outer diameter than the outer diameter D of the second doughnut-shaped ferrite permanent magnet 31 and indirectly abuts against the second ferrite permanent magnet 31 through a plurality of (for example, three) projections 33a spatially arranged along the peripheral edge of said shim 33, thereby reducing the conduction of heat to that side of the shim 33 which faces the second magnet 31. As previously described, the first and second ferrite permanent magnets 30, 31 are formed with substantially the same volume to have an almost equal magnetomotive force. Thus, the first parallelepiped permanent magnet 30 facing the cathode stem has, as previously described, a narrow width and is made long in the horizontal direction as well as in the axial direction of the magnetron body 21, whereas the second doughnut shaped permanent magnet 31 has a larger diameter D and smaller thickness S, thereby striking a balance between their volumes. The reduced thickness of the second doughnut shaped permanent magnet 31 eliminates the necessity of unduly elongating the antenna 28a of the output antenna section 28. A space is provided between the underside of the first magnet 30 and the upper side 29a of the plural radiator plates 29 as well as between the upper side of the second magnet 31 and the underside 29b of said radiator plates 29. Accordingly, cooling air is spread all over the radiator plates 29 for better cooling of the second magnet 31. The shield 36 has its periphery fitted with a tightening band 43 securely to set the parts of the magnetron device in place.

As mentioned above, the magnetron device of this invention, wherein the first magnet 30 facing the cathode stem and yoke member 34 have a width substan tially equal to the outer diameter of the magnetron body 21 and the radiator plates 29 are so arranged as to conduct cooling air in the axial direction of the magnetron body 21 can be more effectively cooled, particularly enabling the thin larger diameter second magnet 31 disposed on the output antenna side to be fully exposed to cooling air for better cooling.

Where a magnetron device is used, for example, with an electronic oven, the heating chamber wall of said oven generally has its temperature considerably raised when the heating chamber contains a small amount of load, leading to the increased temperature of a magnet disposed particularly on the output antenna side. With the magnetron device of this invention, however, the second magnetron is effectively cooled as previously described and is saved from the harmful effect of elevated temperature.

Referring to another embodiment of this invention of FIG. 6, the second magnet 31 is made thinner than the first magnet 30 with a difference in the volumes of both magnets and consequently in the magnetomotive forces generated thereby. However, these different magnetomotive forces do not practically exert any large harmful effect on the magnetron device.

With the magnetron device of this invention, the first permanent magnet and yoke abutting thereagainst have a width equal to the outer diameter of the magnetron body, enabling cooling air to pass easily between the numerous radiator units radially erected around the magnetron body for their effective cooling.

What we claim is:

1. A magnetron device which comprises a magnetron body having a cathode stem and output antenna section respectively provided on both sides of said magnetron body so as to project outward therefrom;

a first ferrite permanent magnet of a parallelpiped shape having a width approximating the diameter of the magnetron body and disposed thereon, with said projecting cathode stern inserted into said first magnet;

a second ferrite permanent magnet of a doughnut shape having a volume substantially equal to that of the first magnet and being disposed on the magnetron body with said projecting output antenna stem inserted into said second magnet;

two shim plates, each interposed between one end face of the respective magnets and the end face of the magnetron body;

a yoke, one member of which is disposed on the first magnet and the other member of which is disposed on the second magnet for magnetic connection of both magnets, the upper wall of said one yoke member abutting against the other end face of the first magnet having a shape substantially equal to the end face of the first magnet;

a radiator provided on the peripheral wall of the magnetron body so as to conduct a cooling medium in the axial direction of the magnetron body; and

a microwave shield so provided as to enclose the cathode stem.

2. A magnetron device according to claim 1, wherein the second magnet has a larger diameter than the outer diameter of the magnetron body and is made thinner than the first magnet.

3. A magnetron device according to claim 1, wherein said shim plates are made of magnetic material and provided with a plurality of small projection for abutment against the magnets.

4. A magnetron device according to claim 1, wherein a space is provided between the underside of the first magnet and the upper side of the radiator facing said first magnet 5. A magnetron device according to claim 1, wherein the first and second magnets are so disposed as to cause the planes of opposite polarity to face each other.

6. A magnetron device according to claim 1, wherein the radiator comprises a plurality of plates radially erected on the periphery of the magnetron body in the axial direction thereof.

7. A magnetron device according to claim 1, wherein said first yoke member is formed with a width approximating that of the first magnet and is made thicker than the second yoke member which is formed with a larger surface area than the first yoke member, and said first and second yoke members are coupled to each other to constitute a magnetic circuit. 

1. A magnetron device which comprises a magnetron body having a cathode stem and output antenna section respectively provided on both sides of said magnetron body so as to project outward therefrom; a first ferrite permanent magnet of a parallelpiped shape having a width approximating the diameter of the magnetron body and disposed thereon, with said projecting cathode stem inserted into said first magnet; a second ferrite permanent magnet of a doughnut shape having a volume substantially equal to that of the first magnet and being disposed on the magnetron body with said projecting output antenna stem inserted into said second magnet; two shim plates, each interposed between one end face of the respective magnets and the end face of the magnetron body; a yoke, one member of which is disposed on the first magnet and the other member of which is disposed on the second magnet for magnetic connection of both magnets, the upper wall of said one yoke member abutting against the other end face of the first magnet having a shape substantially equal to the end face of the first magnet; a radiator provided on the peripheral wall of the magnetron body so as to conduct a cooling medium in the axial direction of the magnetron body; and a microwave shield so provided as to enclose the cathode stem.
 2. A magnetron device according to claim 1, wherein the second magnet has a larger diameter than the outer diameter of the magnetron body and is made thinner than the first magnet.
 3. A magnetron device according to claim 1, wherein said shim plates are made of magnetic material and provided with a plurality of small projection for abutment against the magnets.
 4. A magnetron device according to claim 1, wherein a space is provided between the underside of the first magnet and the upper side of the radiator facing said first magnet
 5. A magnetron device according to claiM 1, wherein the first and second magnets are so disposed as to cause the planes of opposite polarity to face each other.
 6. A magnetron device according to claim 1, wherein the radiator comprises a plurality of plates radially erected on the periphery of the magnetron body in the axial direction thereof.
 7. A magnetron device according to claim 1, wherein said first yoke member is formed with a width approximating that of the first magnet and is made thicker than the second yoke member which is formed with a larger surface area than the first yoke member, and said first and second yoke members are coupled to each other to constitute a magnetic circuit. 